It is well known in the glass art to coat glass sheets with metallic and/or dielectric materials, to impart enhanced solar and optical properties to the glass sheets. For example, it is known to place multiple films (layers) of metals and dielectrics onto glass to produce electrically conductive coatings which are transparent to visible light and highly reflective to infrared radiation. It is also known to deposit conductive metal oxides onto glass, such as, for example, fluorine-doped tin oxide, which are also highly reflective to infrared radiation.
Tungsten oxide is a transparent semi-conductor, which when doped with a material such as fluorine shows an appreciable increase in the infra-red absorption and reflection. Hence, such doped tungsten oxide films, e.g., when applied to glass substrates, are potential candidates for solar control applications.
Many conventional methods for depositing coatings onto glass sheets are known. Examples of conventional deposition processes include liquid or power spray pyrolysis, wherein liquids or solid particles containing film forming reactants are sprayed onto the surface of a hot glass ribbon being produced by the well-known float glass process. A more convenient method for depositing coatings onto glass is by way of chemical vapor deposition (CVD), wherein vaporized film-forming precursors are reacted at or near the surface of a hot glass ribbon to form the metal or dielectric film thereon. Chemical vapor deposition does not suffer from the problems associated with either liquid or power spray pyrolysis processes. That is, a liquid spray pyrolysis process substantially cools the hot glass ribbon, while power spray pyrolysis requires a complex, delicate powered handling and delivery system.
Tungsten oxide films are doped with fluorine by including a fluorinated compound as one of the reactants used in, e.g., the pyrolysis or CVD processes. Once such method for forming a fluorine doped tungsten oxide film on glass is disclosed in U.S. application Ser. No. 07/806,177 entitled "Preparation of Fluorine-Doped Tungstic Oxide" filed Dec. 13, 1991 to Proscia, commonly assigned with the present invention. It discloses forming a coating on glass by reacting at the surface of the glass at elevated temperature: tungsten hexafluoride, and an oxygen containing compound, and a fluorine compound.
It would be desirable to prepare a fluorine-modified tungsten oxide film having the above properties by a process which comprises subjecting an already applied film of tungsten oxide to a fluorine material. Such a process advantageously would allow for the use of techniques such as sputtering, which are particularly suitable for coating curved pieces of glass, to be used to apply the tungsten oxide coating on the substrate. Sputtering equipment is not generally compatible with fluorine-containing compounds.